The present invention relates to a device for storage and conveyance of bulky holders, in particular containers.
Container terminals are generally known and are used for the temporary storage and subsequent distribution of containers, which are brought into a seaport in large numbers in, for example, container ships, and are then transported further by rail in goods trains, by road in lorries or on waterways in smaller vessels. In order to permit temporary storage of the large quantity of containers, said containers are stacked on top of one another in rows spaced apart in a storage yard, generally with the aid of mobile gantry cranes operated by crane drivers. The free space between the rows is necessary for the tracks along which the mobile cranes can move. When a particular container from such a stack has to be transported further, the containers stacked on top of this particular container first have to be moved to a free position before the particular container can be removed from the stack and delivered for further distribution to a generally centrally situated discharge point. Such movements take a relatively large amount of time. Moreover, it is found in practice that a container, once stored, is often moved about ten times before it is removed from the storage site. However, each movement usually has to be paid for, which incurs additional costs. Furthermore, the space is being used inefficiently, since aisles are needed between the rows for the gantry cranes.
The same problem occurs in distribution centres, where pallets or other holders filled with goods are stored temporarily on racks comprising several levels. Here again, aisles have to be present between the racks and at their ends, for forklift trucks or the like which supply and remove the pallets. A large amount of floor space is therefore needed. However, the pallets are not stacked directly on top of one another and can therefore be removed individually from the racks.
A solution known from the trade is described in, for example, WO 94/06708, which discloses a storage system for bulky holders, in particular containers used in aircraft. This system consists of a number of storage levels, each consisting of mutually parallel, individually operable endless horizontal longitudinal conveyors with storage bays for the stored holders. On each level, provision is made for (endless) transverse conveyors at least at the two ends of the horizontal longitudinal conveyors. Aisles between the horizontal longitudinal conveyors are therefore not required.
A disadvantage of such a system is that separate drives, such as chain drives, are needed for each conveyor, as are separate intermediate parts, for example roller conveyors, for transferring a container from a longitudinal conveyor to a transverse conveyor.
EP-A-0 145 871 also discloses a device for the storage and conveyance of containers, in which a so-called “Doppelfahrwagen” (double carriage), which can travel along a network of rails provided with crossover points, is used. Such a carriage is provided with a first travelling mechanism comprising several sets of first travelling wheels, for movement in a first direction, and with a second travelling mechanism comprising several sets of second travelling wheels, for movement in another direction, generally transversely to the first direction, the travelling mechanisms being adjustable in height relative to each other, so that when the first travelling mechanism is resting on the rails and the second has been retracted the carriage with load can move in the first direction, and vice versa. The change in direction of movement can be made at the crossover points. This means that turntables, bends and the like in the network are not needed. These carriages known from EP-A 0 145 871 are provided with a lifting table, so that no additional aids, such as cranes and the like, are needed for loading and unloading.
Disadvantages of this known system are that drives are needed for moving the carriages, and that each carriage has to be provided with a double travelling mechanism.